Step-by-step explanation:
the cost for n shirts is c=15+9(n-1)
c=15+9n-9 simplify
c=9n+6
n represents the number of shirts
so for the cost of 2 shirts, n=2
c=9(2)+6
c=24
therefore it costs $24 for 2 shirts
for the cost of 5 shirts, n=5
c=9(5)+6
c=51
therefore the cost of 5 shirts is $51
1 shirt = $15
2 shirts =$24
3 shirts =$33
24-15 =9
33-24=9
so 9 is the common difference which means each additional shirt is $9 more than the price of all the previous shirts
